Yes, you can void shipments, within a certain time-frame.
Voiding a shipment effectively returns the voided order to Awaiting Shipment status. Once voided, the record will bear a strike-through, meaning you can't do anything else with the record anymore. It is as if the record had been deleted, except that Skubana retains a copy for record purposes. If you ship the order again, it will create a separate record within Skubana.
To void a shipment, go to the Shipments module, search for the record you want to void, highlight the record on the list, then click Void Shipment at the top. Click Void Shipment again when asked to confirm the action.